Dynamics of natural afforestation in Provence

Abstract

The French Mediterranean region, particularly marked by large-scale abandoning of agricultural land since the beginning of the 20th century, is particularly suitable for studying the dynamics of natural reforestation after cultivation has ceased. The models include various pre-forest and forest formations with an expansionist demographic strategy, representing the most remarkable situations as far as growth is concerned. Among these models, three categories can be distinguished: i) expansionist with fast colonisation, ii) expansionist with fast and long-term colonisation, iii) expansionist with a zoochoric determinism. These three models appear successively after cultivation and/or after fire, through their accompanying flora are differentiated according to geographical zones from Basse Provence up to the Mediterranean Alps. All three models feature the production of a high biovolume and abundant representation in space, whether the vegetation consists of bushes or forest species. For milieus with high constraints because of recurrent disturbances, the ligneous population adopts resistance models. These are differentiated from the expansionist models by a much longer generation time with narrower spreading (variable from year to year), high rate of renewal (high aptitude for pruning and development of axillary systems), and low inter-species competition (by wide occupation of space by a few dominant individuals). In the case of neglected forests or long-abandoned cultivation without disturbance, the growth of the vegetation can be covered by a stabilising model, which in the Mediterranean region results in the installation and development of permanent pubescent oak forests. Finally, beyond the phytoecological analysis of the dynamics of forest populations, the statistics of agricultural and forest areas as well as the study of the main social changes help to illustrate and fine-line the interpretation of the models presented, particularly through spectacular progression of expansionist conifers and deciduous oaks over the last century as well as deep-going transformations in the methods of using the soil.